The present invention relates to an image display apparatus and, more particularly, to a spectacle-type image display apparatus which is designed to project an image directly on the retinas in both the user's eyes.
Most image information is generally projected on a monitor, a screen, etc. However, spectacle-type image display apparatuses have also already been proposed. One such display apparatus is disclosed in Japanese Patent Application Laid-Open (KOKAI) No. 3-214872 (1991). In the disclosed'display apparatus, an image of a transmissive image plate, which is illuminated by a point source, is focused on an eyeball by an ocular lens, thereby enabling the user to view the image formed directly on the retina.
The prior art will be explained below with reference to FIG. 17. As shown in the figure, the prior art image display apparatus comprises a point source 111, an image plate 112 illuminated by the point source 111, and a short-focus ocular lens 113 disposed substantially integral with the image plate 112. A beam of light converges to a focus on a pupil 117 lying in front of a crystalline lens 116 in an eyeball 114, and an image is formed on a retina 115 through a pinhole defined by the point of focus. With this arrangement, the frames of the spectacles can be made compact advantageously.
In the above-described prior art, a transmissive liquid crystal plate with a color filter is employed as the image plate 112. However, since the image plate 112 is not in conjugate relation to the retina 115, it is necessary in order to obtain a high-definition image to reduce the diameter of the pinhole formed on the pupil 117 from the viewpoint of geometrical optics. However, if the diameter of the pinhole is made excessively small, the projected image becomes unsharp due to the diffraction of light. Consequently, the above-described prior art cannot provide a high-definition image.